Enhanced yaw rate trailer angle detection initialization

ABSTRACT

A trailer backup assist system for a vehicle reversing a trailer includes a sensor module adapted to attach to the trailer and generate a trailer yaw rate or a trailer speed. The trailer backup assist system also includes a vehicle sensor system that generates a vehicle yaw rate and a vehicle speed. Further, the trailer backup assist system includes a controller that estimates a hitch angle based on the trailer yaw rate or the trailer speed and the vehicle yaw rate and the vehicle speed in view of a kinematic relationship between the trailer and the vehicle.

The present application is related to U.S. patent application Ser. No.14/972,761, entitled “HITCH ANGLE DETECTION FOR TRAILER BACKUP ASSISTSYSTEM,” filed on Dec. 17, 2015, U.S. patent application Ser. No.13/448,529, entitled “VEHICLE TRAILER ANGLE DETECTION SYSTEM ANDMETHOD,” filed on Sep. 15, 2015, U.S. patent application Ser. No.______, entitled “VEHICLE HITCH DETECTION SYSTEM AND METHOD,” filed onJun. 20, 2016, U.S. patent application Ser. No. 14/972,831, entitled“MULTI-STAGE SOLUTION FOR TRAILER HITCH ANGLE INITIALIZATION,” filed onDec. 17, 2015, U.S. patent application Ser. No. 14/736,391, entitled“TRAILER LENGTH ESTIMATION METHOD USING TRAILER YAW RATE SIGNAL,” filedon Jun. 11, 2015, U.S. Pat. No. 8,068,019, entitled “TRAILERIDENTIFICATION SYSTEM,” issued on Nov. 29, 2011, U.S. Pat. No.9,037,349, entitled “TRAILER IDENTIFICATION SYSTEM FOR TRAILER BACKUPASSIST,” issued on May 19, 2015, U.S. Pat. No. 9,340,228, entitled“TRAILER MOTION AND PARAMETER ESTIMATION SYSTEM,” issued on May 17,2016, U.S. Pat. No. 9,315,212, entitled “TRAILER SENSOR MODULE ANDASSOCIATED METHOD OF WIRELESS TRAILER,” issued on Apr. 19, 2016, U.S.Pat. No. 9,102,271, entitled “TRAILER MONITORING SYSTEM AND METHOD,”issued on Aug. 11, 2015, the entire contents of each being incorporatedherein by reference.

FIELD OF THE INVENTION

The disclosure made herein relates generally to vehicles includingtrailer backup assist systems, and more particularly to traileridentification and hitch angle estimation for a trailer at vehiclestart-up.

BACKGROUND OF THE INVENTION

Reversing a vehicle while towing a trailer can be challenging for manydrivers, particularly for drivers that drive with a trailer on aninfrequent basis or with various types of trailers. Systems used toassist a driver with backing a trailer may estimate the position of thetrailer relative to the vehicle utilizing a yaw rate sensor and analgorithm that calculates a hitch angle from yaw rate data.

SUMMARY OF THE INVENTION

A vehicle including a trailer backup assist system includes anauthentication device that permits vehicle operation if theauthentication device is actuated to an ON state from an OFF state. Theauthentication device may comprise a conventional ignition key cylinderthat is actuated utilizing a key, or the authentication device maycomprise a wireless device that provides an authentication code or othersecurity measures. The vehicle also includes a sensor or other featurethat is configured to indicate whether or not a trailer is attached tothe vehicle. The sensor may comprise a switch that provides a signal tothe trailer backup assist system if a trailer is connected to thevehicle. The vehicle further includes a controller configured to storetrailer data, a vehicle position, and hitch angle if the authenticationdevice changes from an ON state to an OFF state to define a power offevent. The controller is also configured to determine if theauthentication device is changed from an OFF state to an ON state todefine a power on event. The controller is also configured to determineif a trailer is connected to the vehicle if a power on event occurs. Thecontroller also determines if a present position of the vehicle haschanged since a power off event. If a present position of the vehiclehas not changed, the controller is configured to retrieve at least oneof trailer data and hitch angle for use in the trailer backup assistsystem. If a present position of the vehicle has not changed since apower off event, the controller provides an indication to a user thattrailer data needs to be supplied to the trailer backup assist system.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a top perspective view of a vehicle attached to a trailer withone embodiment of a hitch angle sensor for operating a trailer backupassist system;

FIG. 2 is a block diagram illustrating one embodiment of the trailerbackup assist system having a steering input device, a curvaturecontroller, and a trailer braking system;

FIG. 3 is a schematic diagram that illustrates the geometry of a vehicleand a trailer overlaid with a two-dimensional x-y coordinate system,identifying variables used to determine a kinematic relationship of thevehicle and the trailer for the trailer backup assist system, accordingto one embodiment;

FIG. 4 is a schematic block diagram illustrating portions of a curvaturecontroller, according to an additional embodiment, and other componentsof the trailer backup assist system, according to such an embodiment;

FIG. 5 is schematic block diagram of the curvature controller of FIG. 4,showing the feedback architecture and signal flow of the curvaturecontroller, according to such an embodiment;

FIG. 6 is a schematic diagram showing a relationship between a hitchangle and a steering angle of the vehicle as it relates to curvature ofthe trailer and a jackknife angle;

FIG. 7 is a plan view of a steering input device having a rotatable knobfor operating the trailer backup assist system, according to oneembodiment;

FIG. 8 is a plan view of another embodiment of a rotatable knob forselecting a desired curvature of a trailer and a corresponding schematicdiagram illustrating a vehicle and a trailer with various trailercurvature paths correlating with desired curvatures that may beselected;

FIG. 9 is a schematic diagram showing a backup sequence of a vehicle anda trailer implementing various curvature selections with the trailerbackup assist system, according to one embodiment;

FIG. 10 is a flow diagram illustrating a method of operating a trailerbackup assist system using an operating routine for steering a vehiclereversing a trailer with normalized control of the desired curvature,according to one embodiment;

FIG. 11 is a schematic diagram that illustrates the geometry of avehicle and a trailer overlaid with a two-dimensional x-y coordinatesystem, identifying variables used to determine a hitch angle, accordingto one embodiment;

FIG. 12 is a flow diagram illustrating a method of estimating a hitchangle using a hitch angle estimation routine, according to oneembodiment;

FIG. 13 is a flow diagram illustrating a method of identifying a trailerand estimating a hitch angle at vehicle start-up; and

FIG. 14 is a partially fragmentary top plan view of a trailer anglemeasurement device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For purposes of description herein, it is to be understood that thedisclosed trailer backup assist system and the related methods mayassume various alternative embodiments and orientations, except whereexpressly specified to the contrary. It is also to be understood thatthe specific devices and processes illustrated in the attached drawings,and described in the following specification are simply exemplaryembodiments of the inventive concepts defined in the appended claims.While various aspects of the trailer backup assist system and therelated methods are described with reference to a particularillustrative embodiment, the disclosed invention is not limited to suchembodiments, and additional modifications, applications, and embodimentsmay be implemented without departing from the disclosed invention.Hence, specific dimensions and other physical characteristics relatingto the embodiments disclosed herein are not to be considered aslimiting, unless the claims expressly state otherwise.

As discussed in more detail below, the system and method 200 of FIG. 13may be utilized in connection with the system and processes of FIGS.1-12 at vehicle start-up to identify a trailer and retrieve trailer dataand/or to provide an initial hitch (trailer) angle at vehicle start up.

Referring to FIGS. 1-12, reference numeral 10 generally designates atrailer backup assist system for controlling a backing path of a trailer12 attached to a vehicle 14 by allowing a driver of the vehicle 14 tospecify a desired curvature 26 of the backing path of the trailer 12. Inone embodiment, the trailer backup assist system 10 automatically steersthe vehicle 14 to guide the trailer 12 on the desired curvature orbacking path 26 as a driver uses the accelerator and brake pedals tocontrol the reversing speed of the vehicle 14. To monitor the positionof the trailer 12 relative to the vehicle 14, the trailer backup assistsystem 10 may include a sensor system 16 that senses or otherwisedetermines a hitch angle γ between the trailer 12 and the vehicle 14. Inone embodiment, the sensor system 16 may include a sensor module 20attached to the trailer 12 that monitors the dynamics of the trailer 12,such as yaw rate, and communicates with a controller 28 of the trailerbackup assist system 10 to determine the instantaneous hitch angle γ.Accordingly, one embodiment of a sensor module 20 is adapted to attachto the trailer 12 and generate a trailer yaw rate ω₂. The trailer backupassist system 10 according to such an embodiment may also include avehicle sensor system 17 that generates a vehicle yaw rate ω₁ and avehicle speed v₁. The controller 28 of the trailer backup assist system10 may thereby estimates a hitch angle γ based on the trailer yaw rateω₂, the vehicle yaw rate ω₁, and the vehicle speed v₁ in view of akinematic relationship between the trailer 12 and the vehicle 14. Inanother embodiment, the sensor system 16 may include a hitch anglesensor 44, such as a vision-based system that employs a camera 46 on thevehicle 14 to monitor a target 52 on the trailer 12 to determine thehitch angle γ and thereby further increase reliability of the overallestimated hitch angle γ.

With respect to the general operation of the trailer backup assistsystem 10, a steering input device 18 may be provided, such as arotatable knob 30, for a driver to provide the desired curvature 26 ofthe trailer 12. As such, the steering input device 18 may be operablebetween a plurality of selections, such as successive rotated positionsof a knob 30, that each provide an incremental change to the desiredcurvature 26 of the trailer 12. Upon inputting the desired curvature 26,the controller may generate a steering command for the vehicle 14 toguide the trailer 12 on the desired curvature 26 based on the estimatedhitch angle γ and a kinematic relationship between the trailer 12 andthe vehicle 14. Therefore, the accuracy of the hitch angle estimation iscritical to operating the trailer backup assist system 10. However, itis appreciated that such a system for instantaneously estimating hitchangle may be used in association with additional or alternative vehiclefeatures, such as trailer sway monitoring.

With reference to the embodiment shown in FIG. 1, the vehicle 14 is apickup truck embodiment that is equipped with one embodiment of thetrailer backup assist system 10 for controlling the backing path of thetrailer 12 that is attached to the vehicle 14. Specifically, the vehicle14 is pivotally attached to one embodiment of the trailer 12 that has abox frame 32 with an enclosed cargo area 34, a single axle having aright wheel assembly and a left wheel assembly, and a tongue 36longitudinally extending forward from the enclosed cargo area 34. Theillustrated trailer 12 also has a trailer hitch connector in the form ofa coupler assembly 38 that is connected to a vehicle hitch connector inthe form of a hitch ball 40. The coupler assembly 38 latches onto thehitch ball 40 to provide a pivoting ball joint connection 42 that allowsfor articulation of the hitch angle γ. It should be appreciated thatadditional embodiments of the trailer 12 may alternatively couple withthe vehicle 14 to provide a pivoting connection, such as by connectingwith a fifth wheel connector. It is also contemplated that additionalembodiments of the trailer may include more than one axle and may havevarious shapes and sizes configured for different loads and items, suchas a boat trailer or a flatbed trailer.

Still referring to FIG. 1, the sensor system 16 in the illustratedembodiment includes both a sensor module 20 and a vision-based hitchangle sensor 44 for estimating the hitch angle γ between the vehicle 14and the trailer 12. The illustrated hitch angle sensor 44 employs acamera 46 (e.g. video imaging camera) that may be located proximate anupper region of the vehicle tailgate 48 at the rear of the vehicle 14,as shown, such that the camera 46 may be elevated relative to the tongue36 of the trailer 12. The illustrated camera 46 has an imaging field ofview 50 located and oriented to capture one or more images of thetrailer 12, including a region containing one or more desired targetplacement zones for at least one target 52 to be secured. Although it iscontemplated that the camera 46 may capture images of the trailer 12without a target 52 to determine the hitch angle γ, in the illustratedembodiment, the trailer backup assist system 10 includes a target 52placed on the trailer 12 to allow the trailer backup assist system 10 toutilize information acquired via image acquisition and processing of thetarget 52. For instance, the illustrated camera 46 may include a videoimaging camera that repeatedly captures successive images of the trailer12 that may be processed to identify the target 52 and its location onthe trailer 12 for determining movement of the target 52 and the trailer12 relative to the vehicle 14 and the corresponding hitch angle γ. Itshould also be appreciated that the camera 46 may include one or morevideo imaging cameras and may be located at other locations on thevehicle 14 to acquire images of the trailer 12 and the desired targetplacement zone, such as on a passenger cab 54 of the vehicle 14 tocapture images of a gooseneck trailer. Furthermore, it is contemplatedthat additional embodiments of the hitch angle sensor 44 and the sensorsystem 16 for providing the hitch angle γ may include one or acombination of a potentiometer, a magnetic-based sensor, an opticalsensor, a proximity sensor, a rotational sensor, a capacitive sensor, aninductive sensor, or a mechanical based sensor, such as a mechanicalsensor assembly mounted to the pivoting ball joint connection 42, energytransducers of a reverse aid system, a blind spot system, and/or a crosstraffic alert system, and other conceivable sensors or indicators of thehitch angle γ to supplement or be used in place of the vision-basedhitch angle sensor 44.

The embodiment of the sensor module 20 illustrated in FIG. 1 includes ahoused sensor cluster 21 mounted on the tongue 36 of the trailer 12proximate the enclosed cargo area 34 and includes left and right wheelspeed sensors 23 on laterally opposing wheels of the trailer 12. It isconceivable that the wheel speed sensors 23 may be bi-directional wheelspeed sensors for monitoring both forward and reverse speeds. Also, itis contemplated that the sensor cluster 21 in additional embodiments maybe mounted on alternative portions of the trailer 12.

The sensor module 20 generates a plurality of signals indicative ofvarious dynamics of the trailer 12. The signals may include a yaw ratesignal, a lateral acceleration signal, and wheel speed signals generatedrespectively by a yaw rate sensor 25, an accelerometer 27, and the wheelspeed sensors 23. Accordingly, in the illustrated embodiment, the yawrate sensor 25 and the accelerometer 27 are contained within the housedsensor cluster 21, although other configurations are conceivable. It isconceivable that the accelerometer 27, in some embodiments, may be twoor more separate sensors and may be arranged at an offset angle, such astwo sensors arranged at plus and minus forty-five degrees from thelongitudinal direction of the trailer or arranged parallel with thelongitudinal and lateral directions of the trailer, to generate a morerobust acceleration signal. It is also contemplated that these sensorsignals could be compensated and filtered to remove offsets or drifts,and smooth out noise. Further, the controller 28 may utilizes processedsignals received outside of the sensor system 16, including standardsignals from the brake control system 72 and the power assist steeringsystem 62, such as vehicle yaw rate ω₁, vehicle speed v₁, and steeringangle δ, to estimate the trailer hitch angle γ, trailer speed, andrelated trailer parameters. As described in more detail below, thecontroller 28 may estimate the hitch angle γ based on the trailer yawrate ω₂, the vehicle yaw rate ω₁, and the vehicle speed v₁ in view of akinematic relationship between the trailer 12 and the vehicle 14. Thecontroller 28 of the trailer backup assist system 10 may also utilizethe estimated trailer variables and trailer parameters to control thesteering system 62, brake control system 72, and the powertrain controlsystem 74, such as to assist backing the vehicle-trailer combination orto mitigate a trailer sway condition.

In general, sensor module 20 may be installed on trailer 12, and thesensor module 20 may remain on the trailer 12 after trailer 12 isdisconnected from vehicle 14. As discussed in more detail below inconnection with FIG. 13, one or more of the sensors 23, 25, 27 of sensormodule 20 may transmit serial numbers and/or other unique identifyinginformation to the trailer backup assist system 10 (e.g. controller 28)such that the trailer backup assist system can determine if trailer 12is a “known” trailer and thereby identify a specific trailer 12. Thetrailer backup assist system 10 can then retrieve stored trailer data(e.g. trailer length, trailer type, etc.) for a specific trailer 12. Ifa particular vehicle 14 is regularly used to tow several differenttrailers 12, a sensor module 20 with unique serial numbers or otheridentifying code/information may be mounted on each trailer 12.Alternatively, a target 52 (FIG. 1) including unique identificationinformation (e.g. a bar code) may be placed on each trailer 12 that isused with a specific vehicle 14 to thereby enable the trailer backupassist system 10 of the vehicle 14 to identify each trailer.

With reference to the embodiment of the trailer backup assist system 10shown in FIG. 2, the hitch angle sensor 44 is provided in dashed linesto illustrate that in some embodiments it may be omitted when thetrailer sensor module 20 is provided. The illustrated embodiment of thetrailer backup assist system 10 receives vehicle and trailerstatus-related information from additional sensors and devices. Thisinformation includes positioning information from a positioning device56, which may include a global positioning system (GPS) on the vehicle14 or a handled device, to determine a coordinate location of thevehicle 14 and the trailer 12 based on the location of the positioningdevice 56 with respect to the trailer 12 and/or the vehicle 14 and basedon the estimated hitch angle γ. The positioning device 56 mayadditionally or alternatively include a dead reckoning system fordetermining the coordinate location of the vehicle 14 and the trailer 12within a localized coordinate system based at least on vehicle speed,steering angle, and hitch angle γ. Other vehicle information received bythe trailer backup assist system 10 may include a speed of the vehicle14 from a speed sensor 58 and a yaw rate of the vehicle 14 from a yawrate sensor 60. It is contemplated that in additional embodiments, thehitch angle sensor 44 and other vehicle sensors and devices may providesensor signals or other information, such as proximity sensor signals orsuccessive images of the trailer 12, that the controller of the trailerbackup assist system 10 may process with various routines to determinean indicator of the hitch angle γ, such as a range of hitch angles.

With reference to FIG. 2, vehicle 14 may include an authenticationdevice 202. Authentication device 202 may comprise a conventionalignition key cylinder that provides an “ON” signal or state if a key isinserted and rotated to turn the vehicle on. Alternatively,authentication device 202 may comprise a wireless device that isconfigured to permit operation of vehicle 14 and provide an “ON”(vehicle power on) state if an authorized security code is received froma wireless transmitter (fob), smartphone, or other device. When a userturns off vehicle 14, authentication device 202 provides an “OFF”(vehicle power off) state. Actuating authentication device 202 to turnon vehicle 14 and change from an OFF state to an ON state provides a“KEY ON” (vehicle power turned on) event, and deactuation ofauthentication device 202 to turn off vehicle 14 changes the state fromON to OFF to provide a “KEY OFF” (vehicle power turned off) event. Itwill be understood that the terms “ON,” “OFF,” “KEY ON,” and “KEY OFF”are not limited to any particular type of authentication device 202.Thus, a key is not required to provide “KEY ON” and “KEY OFF” events orstates, and these terms are generally used to refer to conditions inwhich a vehicle is turned on/off and may also be authorized to permitvehicle operation. In general, vehicle 14 may be configured such thatelectrical power is supplied to system 10 when vehicle power is on, andelectrical power is not supplied to system 10 when vehicle power isturned off. System 10 may be configured to operate when vehicle power isturned on and off as discussed in more detail below in connection withFIG. 13. As discussed in more detail below in connection with FIG. 13,signals/data from authentication device 202 may be utilized to controlstorage and/or retrieval of trailer data, trailer identificationinformation, and other functions of system 10 at vehicle start-up andshut-down.

Vehicle 14 and/or trailer 12 may optionally include a sensor 204 thatprovides a signal to trailer backup assist system 10 indicating that atrailer 12 is connected to vehicle 14. Sensor 204 may comprise a switchor the like that is actuated to provide a TrailerConnected Flag=TRUEsignal (see also FIG. 13) if a hitch ball 40 is received in couplerassembly 38. The trailer backup assist system may also be configured todetermine if communication with one or more of sensors 23, 25, and 27 oftrailer sensor module 20 has been established, and provide aTrailerConnected Flag=TRUE signal if communication has been established.If the trailer backup assist system is configured in this way, sensor204 is not required. If a sensor 204 is utilized, the trailer backupassist system may be configured to generate an alert (e.g. a message onscreen 82) if sensor 204 indicates that a trailer is connected but thetrailer backup assist system is unable to establish communication withsensor module 20. For example, a message such as “trailer sensor modulenot operating properly” could be displayed on screen 82.

As further shown in FIG. 2, one embodiment of the trailer backup assistsystem 10 is in communication with a power assist steering system 62 ofthe vehicle 14 to operate the steered wheels 64 (FIG. 1) of the vehicle14 for moving the vehicle 14 in such a manner that the trailer 12 reactsin accordance with the desired curvature 26 of the trailer 12. In theillustrated embodiment, the power assist steering system 62 is anelectric power-assisted steering (EPAS) system that includes an electricsteering motor 66 for turning the steered wheels 64 to a steering anglebased on a steering command, whereby the steering angle may be sensed bya steering angle sensor 67 of the power assist steering system 62. Thesteering command may be provided by the trailer backup assist system 10for autonomously steering during a backup maneuver and may alternativelybe provided manually via a rotational position (e.g., steering wheelangle) of a steering wheel 68 (FIG. 1). However, in the illustratedembodiment, the steering wheel 68 of the vehicle 14 is mechanicallycoupled with the steered wheels 64 of the vehicle 14, such that thesteering wheel 68 moves in concert with steered wheels 64, preventingmanual intervention with the steering wheel 68 during autonomoussteering. More specifically, a torque sensor 70 is provided on the powerassist steering system 62 that senses torque on the steering wheel 68that is not expected from autonomous control of the steering wheel 68and therefore indicative of manual intervention, whereby the trailerbackup assist system 10 may alert the driver to discontinue manualintervention with the steering wheel 68 and/or discontinue autonomoussteering.

In alternative embodiments, some vehicles have a power assist steeringsystem 62 that allows a steering wheel 68 to be partially decoupled frommovement of the steered wheels 64 of such a vehicle. Accordingly, thesteering wheel 68 can be rotated independent of the manner in which thepower assist steering system 62 of the vehicle controls the steeredwheels 64 (e.g., autonomous steering as commanded by the trailer backupassist system 10). As such, in these types of vehicles where thesteering wheel 68 can be selectively decoupled from the steered wheels64 to allow independent operation thereof, the steering wheel 68 may beused as a steering input device 18 for the trailer backup assist system10, as disclosed in greater detail herein.

Referring again to the embodiment illustrated in FIG. 2, the powerassist steering system 62 provides the controller 28 of the trailerbackup assist system 10 with information relating to a rotationalposition of steered wheels 64 of the vehicle 14, including a steeringangle. The controller 28 in the illustrated embodiment processes thecurrent steering angle, in addition to other vehicle 14 and trailer 12conditions to guide the trailer 12 along the desired curvature 26. It isconceivable that the trailer backup assist system 10, in additionalembodiments, may be an integrated component of the power assist steeringsystem 62. For example, the power assist steering system 62 may includea trailer backup assist algorithm for generating vehicle steeringinformation and commands as a function of all or a portion ofinformation received from the steering input device 18, the hitch anglesensor 44, the power assist steering system 62, a vehicle brake controlsystem 72, a powertrain control system 74, and other vehicle sensors anddevices.

As also illustrated in FIG. 2, the vehicle brake control system 72 mayalso communicate with the controller 28 to provide the trailer backupassist system 10 with braking information, such as vehicle wheel speed,and to receive braking commands from the controller 28. For instance,vehicle speed information can be determined from individual wheel speedsas monitored by the brake control system 72. Vehicle speed may also bedetermined from the powertrain control system 74, the speed sensor 58,and the positioning device 56, among other conceivable means. In someembodiments, individual wheel speeds can also be used to determine avehicle yaw rate, which can be provided to the trailer backup assistsystem 10 in the alternative or in addition to the vehicle yaw ratesensor 60. In certain embodiments, the trailer backup assist system 10can provide vehicle braking information to the brake control system 72for allowing the trailer backup assist system 10 to control braking ofthe vehicle 14 during backing of the trailer 12. For example, thetrailer backup assist system 10 in some embodiments may regulate speedof the vehicle 14 during backing of the trailer 12, which can reduce thepotential for unacceptable trailer backup conditions. Examples ofunacceptable trailer backup conditions include, but are not limited to,a vehicle 14 over speed condition, a high hitch angle rate, trailerangle dynamic instability, a calculated theoretical trailer jackknifecondition (defined by a maximum vehicle steering angle, drawbar length,tow vehicle wheelbase, and an effective trailer length), or physicalcontact jackknife limitation (defined by an angular displacement limitrelative to the vehicle 14 and the trailer 12), and the like. It isdisclosed herein that the trailer backup assist system 10 can issue analert signal corresponding to a notification of an actual, impending,and/or anticipated unacceptable trailer backup condition.

The powertrain control system 74, as shown in the embodiment illustratedin FIG. 2, may also interact with the trailer backup assist system 10for regulating speed and acceleration of the vehicle 14 during backingof the trailer 12. As mentioned above, regulation of the speed of thevehicle 14 may be necessary to limit the potential for unacceptabletrailer backup conditions such as, for example, jackknifing and trailerangle dynamic instability. Similar to high-speed considerations as theyrelate to unacceptable trailer backup conditions, high acceleration andhigh dynamic driver curvature requests can also lead to suchunacceptable trailer backup conditions.

With continued reference to FIG. 2, the trailer backup assist system 10in the illustrated embodiment may communicate with one or more devices,including a vehicle alert system 76, which may prompt visual, auditory,and tactile warnings. For instance, vehicle brake lights 78 and vehicleemergency flashers may provide a visual alert and a vehicle horn 79and/or speaker 81 may provide an audible alert. Additionally, thetrailer backup assist system 10 and/or vehicle alert system 76 maycommunicate with a human machine interface (HMI) 80 for the vehicle 14.The HMI 80 may include a vehicle display 82, such as a center-stackmounted navigation or entertainment display (FIG. 1). Further, thetrailer backup assist system 10 may communicate via wirelesscommunication with another embodiment of the HMI 80, such as with one ormore handheld or portable devices, including one or more smartphones.The portable device may also include the display 82 for displaying oneor more images and other information to a user. For instance, theportable device may display one or more images of the trailer 12 and anindication of the estimated hitch angle on the display 82. In addition,the portable device may provide feedback information, such as visual,audible, and tactile alerts.

As further illustrated in FIG. 2, the trailer backup assist system 10includes a steering input device 18 that is connected to the controller28 for allowing communication of information therebetween. It isdisclosed herein that the steering input device 18 can be coupled to thecontroller 28 in a wired or wireless manner. The steering input device18 provides the trailer backup assist system 10 with informationdefining the desired backing path of travel of the trailer 12 for thecontroller 28 to process and generate steering commands. Morespecifically, the steering input device 18 may provide a selection orpositional information that correlates with a desired curvature 26 ofthe desired backing path of travel of the trailer 12. Also, the trailersteering commands provided by the steering input device 18 can includeinformation relating to a commanded change in the path of travel, suchas an incremental change in the desired curvature 26, and informationrelating to an indication that the trailer 12 is to travel along a pathdefined by a longitudinal centerline axis of the trailer 12, such as adesired curvature value of zero that defines a substantially straightpath of travel for the trailer. As will be discussed below in moredetail, the steering input device 18 according to one embodiment mayinclude a movable control input device for allowing a driver of thevehicle 14 to command desired trailer steering actions or otherwiseselect and alter a desired curvature. For instance, the moveable controlinput device may be a rotatable knob 30, which can be rotatable about arotational axis extending through a top surface or face of the knob 30.In other embodiments, the rotatable knob 30 may be rotatable about arotational axis extending substantially parallel to a top surface orface of the rotatable knob 30. Furthermore, the steering input device18, according to additional embodiments, may include alternative devicesfor providing a desired curvature 26 or other information defining adesired backing path, such as a joystick, a keypad, a series ofdepressible buttons or switches, a sliding input device, various userinterfaces on a touch-screen display, a vision based system forreceiving gestures, a control interface on a portable device, and otherconceivable input devices as generally understood by one having ordinaryskill in the art. It is contemplated that the steering input device 18may also function as an input device for other features, such asproviding inputs for other vehicle features or systems.

Still referring to the embodiment shown in FIG. 2, the controller 28 isconfigured with a microprocessor 84 to process logic and routines storedin memory 86 that receive information from the sensor system 16,including the trailer sensor module 20, the hitch angle sensor 44, thesteering input device 18, the power assist steering system 62, thevehicle brake control system 72, the trailer braking system, thepowertrain control system 74, and other vehicle sensors and devices. Thecontroller 28 may generate vehicle steering information and commands asa function of all or a portion of the information received. Thereafter,the vehicle steering information and commands may be provided to thepower assist steering system 62 for affecting steering of the vehicle 14to achieve a commanded path of travel for the trailer 12. The controller28 may include the microprocessor 84 and/or other analog and/or digitalcircuitry for processing one or more routines. Also, the controller 28may include the memory 86 for storing one or more routines, including ahitch angle estimation routine 130, an operating routine 132, and acurvature routine 98. It should be appreciated that the controller 28may be a stand-alone dedicated controller or may be a shared controllerintegrated with other control functions, such as integrated with thesensor system 16, the power assist steering system 62, and otherconceivable onboard or off-board vehicle control systems.

With reference to FIG. 3, we now turn to a discussion of vehicle andtrailer information and parameters used to calculate a kinematicrelationship between a curvature of a path of travel of the trailer 12and the steering angle of the vehicle 14 towing the trailer 12, whichcan be desirable for a trailer backup assist system 10 configured inaccordance with some embodiments, including for use by a curvatureroutine 98 of the controller 28 in one embodiment. To achieve such akinematic relationship, certain assumptions may be made with regard toparameters associated with the vehicle/trailer system. Examples of suchassumptions include, but are not limited to, the trailer 12 being backedby the vehicle 14 at a relatively low speed, wheels of the vehicle 14and the trailer 12 having negligible (e.g., no) slip, tires of thevehicle 14 having negligible (e.g., no) lateral compliance, tires of thevehicle 14 and the trailer 12 having negligible (e.g., no) deformation,actuator dynamics of the vehicle 14 being negligible, and the vehicle 14and the trailer 12 exhibiting negligible (e.g., no) roll or pitchmotions, among other conceivable factors with the potential to have aneffect on controlling the trailer 12 with the vehicle 14.

As shown in FIG. 3, for a system defined by a vehicle 14 and a trailer12, the kinematic relationship is based on various parameters associatedwith the vehicle 14 and the trailer 12. These parameters include:

δ: steering angle at steered front wheels of the vehicle;

α: yaw angle of the vehicle;

β: yaw angle of the trailer;

γ: hitch angle (γ=β−α);

W: wheel base of the vehicle;

L: drawbar length between hitch point and rear axle of the vehicle;

D: distance (trailer length) between hitch point and axle of the traileror effective axle for a multiple axle trailer; and

r₂: curvature radius for the trailer.

One embodiment of a kinematic relationship between trailer path radiusof curvature r₂ at the midpoint of an axle of the trailer 12, steeringangle δ of the steered wheels 64 of the vehicle 14, and the hitch angleγ can be expressed in the equation provided below. As such, if the hitchangle γ is provided, the trailer path curvature κ₂ can be controlledbased on regulating the steering angle δ (where {dot over (β)} istrailer yaw rate and {dot over (η)} is trailer velocity).

$\kappa_{2} = {\frac{1}{r_{2}} = {\frac{\overset{.}{\beta}}{\overset{.}{\eta}} = \frac{{\left( {W + \frac{{KV}^{2}}{g}} \right)\sin \; \gamma} + {L\; \cos \; \gamma \; \tan \; \delta}}{D\left( {{\left( {W + \frac{{KV}^{2}}{g}} \right)\; \cos \; \gamma} - {L\; \sin \; \gamma \; \tan \; \delta}} \right)}}}$

This relationship can be expressed to provide the steering angle δ as afunction of trailer path curvature κ₂ and hitch angle γ.

$\delta = {{\tan^{- 1}\left( \frac{\left( {W + \frac{{KV}^{2}}{g}} \right)\left\lbrack {{\kappa_{2}D\; \cos \; \gamma} - {\sin \; \gamma}} \right\rbrack}{{{DL}\; \kappa_{2}\sin \; \gamma} + {L\; \cos \; \gamma}} \right)} = {F\left( {\gamma,\kappa_{2},K} \right)}}$

Accordingly, for a particular vehicle and trailer combination, certainparameters (e.g., D, W and L) of the kinematic relationship are constantand assumed known. The HMI 80 may include a touchscreen 82, buttons,and/or other input features that can be used by an operator to inputtrailer data (e.g. trailer length D) for a specific trailer 12. V is thevehicle longitudinal speed and g is the acceleration due to gravity. Kis a speed dependent parameter which when set to zero makes thecalculation of steering angle independent of vehicle speed. For example,vehicle-specific parameters of the kinematic relationship can bepredefined in an electronic control system of the vehicle 14 andtrailer-specific parameters of the kinematic relationship can beinputted by a driver of the vehicle 14, determined from sensed trailerbehavior in response to vehicle steering commands, or otherwisedetermined from signals provided by the trailer 12. Trailer pathcurvature κ₂ can be determined from the driver input via the steeringinput device 18. Through the use of the equation for providing steeringangle, a corresponding steering command can be generated by thecurvature routine 98 for controlling the power assist steering system 62of the vehicle 14. As discussed below in connection with FIG. 13, a usermay be prompted to enter trailer data at “KEY ON” if the trailer backupassist system detects that a “new” (unrecognized) trailer 12 isconnected to vehicle 14. Alternatively, the system may automaticallyestimate the trailer angle and trailer parameters while the vehicle andtrailer are driven without using the Trailer Backup Assist system.Otherwise, the user may be prompted to perform a calibration maneuver ifthe Trailer Backup Assist System is activated before sufficient drivingis performed to estimate the trailer angle and trailer parameters.

In an additional embodiment, an assumption may be made by the curvatureroutine 98 that a longitudinal distance L between the pivotingconnection and the rear axle of the vehicle 14 is equal to zero forpurposes of operating the trailer backup assist system 10 when agooseneck trailer or other similar trailer is connected with the a hitchball or a fifth wheel connector located over a rear axle of the vehicle14. The assumption essentially assumes that the pivoting connection withthe trailer 12 is substantially vertically aligned with the rear axle ofthe vehicle 14. When such an assumption is made, the controller 28 maygenerate the steering angle command for the vehicle 14 as a functionindependent of the longitudinal distance L between the pivotingconnection and the rear axle of the vehicle 14. It is appreciated thatthe gooseneck trailer mentioned generally refers to the tongueconfiguration being elevated to attach with the vehicle 14 at anelevated location over the rear axle, such as within a bed of a truck,whereby embodiments of the gooseneck trailer may include flatbed cargoareas, enclosed cargo areas, campers, cattle trailers, horse trailers,lowboy trailers, and other conceivable trailers with such a tongueconfiguration.

Yet another embodiment of the curvature routine 98 of the trailer backupassist system 10 is illustrated in FIG. 4, showing the generalarchitectural layout whereby a measurement module 88, a hitch angleregulator 90, and a curvature regulator 92 are routines that may bestored in the memory 86 of the controller 28. In the illustrated layout,the steering input device 18 provides a desired curvature κ₂ value tothe curvature regulator 92 of the controller 28, which may be determinedfrom the desired backing path 26 that is input with the steering inputdevice 18. The curvature regulator 92 computes a desired hitch angleγ(d) based on the current desired curvature κ₂ along with the steeringangle δ provided by a measurement module 88 in this embodiment of thecontroller 28. The measurement module 88 may be a memory device separatefrom or integrated with the controller 28 that stores data from sensorsof the trailer backup assist system 10, such as the hitch angle sensor44, the vehicle speed sensor 58, the steering angle sensor, oralternatively the measurement module 88 may otherwise directly transmitdata from the sensors without functioning as a memory device. Once thedesired hitch angle γ(d) is computed by the curvature regulator 92 thehitch angle regulator 90 generates a steering angle command based on thecomputed desired hitch angle γ(d) as well as a measured or otherwiseestimated hitch angle γ(m) and a current velocity of the vehicle 14. Thesteering angle command is supplied to the power assist steering system62 of the vehicle 14, which is then fed back to the measurement module88 to reassess the impacts of other vehicle characteristics impactedfrom the implementation of the steering angle command or other changesto the system. Accordingly, the curvature regulator 92 and the hitchangle regulator 90 continually process information from the measurementmodule 88 to provide accurate steering angle commands that place thetrailer 12 on the desired curvature κ₂ and the desired backing path 26,without substantial overshoot or continuous oscillation of the path oftravel about the desired curvature κ₂.

As also shown in FIG. 5, the embodiment of the curvature routine 98shown in FIG. 4 is illustrated in a control system block diagram.Specifically, entering the control system is an input, κ₂, whichrepresents the desired curvature 26 of the trailer 12 that is providedto the curvature regulator 92. The curvature regulator 92 can beexpressed as a static map, p(κ₂, δ), which in one embodiment is thefollowing equation:

${p\left( {\kappa_{2},\delta} \right)} = {\tan^{- 1}\left( \frac{{\kappa_{2}D} + {L\; {\tan (\delta)}}}{{\kappa_{2}{DL}\; {\tan (\delta)}} - W} \right)}$

Where,

κ₂ represents the desired curvature of the trailer 12 or 1/r₂ as shownin FIG. 3;

δ represents the steering angle;

L represents the distance from the rear axle of the vehicle 14 to thehitch pivot point;

D represents the distance from the hitch pivot point to the axle of thetrailer 12; and

W represents the distance from the rear axle to the front axle of thevehicle 14.

With further reference to FIG. 5, the output hitch angle of p(κ₂, δ) isprovided as the reference signal, γ_(ref), for the remainder of thecontrol system, although the steering angle δ value used by thecurvature regulator 92 is feedback from the non-linear function of thehitch angle regulator 90. It is shown that the hitch angle regulator 90uses feedback linearization for defining a feedback control law, asfollows:

${g\left( {u,\gamma,v} \right)} = {\delta = {\tan^{- 1}\left( {\frac{W}{v\left( {1 + {\frac{L}{D}{\cos (\gamma)}}} \right)}\left( {u - {\frac{v}{D}{\sin (\gamma)}}} \right)} \right)}}$

As also shown in FIG. 5, the feedback control law, g(u, γ, v), isimplemented with a proportional integral (PI) controller, whereby theintegral portion substantially eliminates steady-state tracking error.More specifically, the control system illustrated in FIG. 58 may beexpressed as the following differential-algebraic equations:

$\mspace{20mu} {{\overset{.}{\gamma}(t)} = {{\frac{v(t)}{D}{\sin \left( {\gamma (t)} \right)}} + {\left( {1 + {\frac{L}{D}{\cos \left( {\gamma (t)} \right)}}} \right)\frac{v(t)}{W}\overset{\_}{\delta}}}}$${\tan (\delta)} = {\overset{\_}{\delta} = {\frac{W}{{v(t)}\left( {1 + {\frac{L}{D}{\cos \left( {\gamma (t)} \right)}}} \right)}\left( {{K_{P}\left( {{p\left( {\kappa_{2},\delta} \right)} - {\gamma (t)}} \right)} - {\frac{v(t)}{D}{\sin \left( {\gamma (t)} \right)}}} \right)}}$

It is contemplated that the PI controller may have gain terms based ontrailer length D since shorter trailers will generally have fasterdynamics. In addition, the hitch angle regulator 90 may be configured toprevent the desired hitch angle γ(d) to reach or exceed a jackknifeangle γ(j), as computed by the controller or otherwise determined by thetrailer backup assist system 10, as disclosed in greater detail herein.

Referring now to FIG. 6, in the illustrated embodiments of the disclosedsubject matter, it is desirable to limit the potential for the vehicle14 and the trailer 12 to attain a jackknife angle (i.e., thevehicle/trailer system achieving a jackknife condition). A jackknifeangle γ(j) refers to a hitch angle γ that while backing cannot beovercome by the maximum steering input for a vehicle such as, forexample, the steered front wheels of the vehicle 14 being moved to amaximum steered angle δ at a maximum rate of steering angle change. Thejackknife angle γ(j) is a function of a maximum wheel angle for thesteered wheels of the vehicle 14, the wheel base W of the vehicle 14,the distance L between hitch point and the rear axle of the vehicle 14,and the trailer length D between the hitch point and the axle of thetrailer 12 or the effective axle when the trailer 12 has multiple axles.When the hitch angle γ for the vehicle 14 and the trailer 12 achieves orexceeds the jackknife angle γ(j), the vehicle 14 may be pulled forwardto reduce the hitch angle γ. Thus, for limiting the potential for avehicle/trailer system attaining a jackknife angle, it is preferable tocontrol the yaw angle of the trailer 12 while keeping the hitch angle γof the vehicle/trailer system relatively small.

A kinematic model representation of the vehicle 14 and the trailer 12can also be used to determine a jackknife angle for the vehicle-trailercombination. Accordingly, with reference to FIGS. 3 and 6, a steeringangle limit for the steered front wheels requires that the hitch angle γcannot exceed the jackknife angle γ(j), which is also referred to as acritical hitch angle γ. Thus, under the limitation that the hitch angleγ cannot exceed the jackknife angle γ(j), the jackknife angle γ(j) isthe hitch angle γ that maintains a circular motion for thevehicle/trailer system when the steered wheels 64 are at a maximumsteering angle δ(max). The steering angle for circular motion with hitchangle γ is defined by the following equation.

${\tan \; \delta_{\max}} = \frac{w\; \sin \; \gamma_{\max}}{D + {L\; \cos \; \gamma_{\max}}}$

Solving the above equation for hitch angle γ allows jackknife angle γ(j)to be determined. This solution, which is shown in the followingequation, can be used in implementing trailer backup assistfunctionality in accordance with the disclosed subject matter formonitoring hitch angle γ in relation to jackknife angle.

${\cos \; \overset{\_}{\gamma}} = \frac{{- b} \pm \sqrt{b^{2} - {4\; {ac}}}}{2\; a}$

where,

a=L² tan² δ(max)+W²;

b=2 LD tan² δ(max); and

c=D² tan² δ(max)−W².

In certain instances of backing the trailer 12, a jackknife enablingcondition can arise based on current operating parameters of the vehicle14 in combination with a corresponding hitch angle γ. This condition canbe indicated when one or more specified vehicle operating thresholds aremet while a particular hitch angle γ is present. For example, althoughthe particular hitch angle γ is not currently at the jackknife angle forthe vehicle 14 and attached trailer 12, certain vehicle operatingparameters can lead to a rapid (e.g., uncontrolled) transition of thehitch angle γ to the jackknife angle for a current commanded trailercurvature and/or can reduce an ability to steer the trailer 12 away fromthe jackknife angle. One reason for a jackknife enabling condition isthat trailer curvature control mechanisms (e.g., those in accordancewith the disclosed subject matter) generally calculate steering commandsat an instantaneous point in time during backing of a trailer 12.However, these calculations will typically not account for lag in thesteering control system of the vehicle 14 (e.g., lag in a steering EPAScontroller). Another reason for the jackknife enabling condition is thattrailer curvature control mechanisms generally exhibit reduced steeringsensitivity and/or effectiveness when the vehicle 14 is at relativelyhigh speeds and/or when undergoing relatively high acceleration.

Jackknife determining information may be received by the controller 28,according to one embodiment, to process and characterize a jackknifeenabling condition of the vehicle-trailer combination at a particularpoint in time (e.g., at the point in time when the jackknife determininginformation was sampled). Examples of the jackknife determininginformation include, but are not limited to, information characterizingan estimated hitch angle γ, information characterizing a vehicleaccelerator pedal transient state, information characterizing a speed ofthe vehicle 14, information characterizing longitudinal acceleration ofthe vehicle 14, information characterizing a brake torque being appliedby a brake system of the vehicle 14, information characterizing apowertrain torque being applied to driven wheels of the vehicle 14, andinformation characterizing the magnitude and rate of driver requestedtrailer curvature. In this regard, jackknife determining informationwould be continually monitored, such as by an electronic control unit(ECU) that carries out trailer backup assist (TBA) functionality. Afterreceiving the jackknife determining information, a routine may processthe jackknife determining information for determining if thevehicle-trailer combination attained the jackknife enabling condition atthe particular point in time. The objective of the operation forassessing the jackknife determining information is determining if ajackknife enabling condition has been attained at the point in timedefined by the jackknife determining information. If it is determinedthat a jackknife enabling condition is present at the particular pointin time, a routine may also determine an applicable countermeasure orcountermeasures to implement. Accordingly, in some embodiments, anapplicable countermeasure will be selected dependent upon a parameteridentified as being a key influencer of the jackknife enablingcondition. However, in other embodiments, an applicable countermeasurewill be selected as being most able to readily alleviate the jackknifeenabling condition. In still another embodiment, a predefinedcountermeasure or predefined set of countermeasures may be theapplicable countermeasure(s).

As previously disclosed with reference to the illustrated embodiments,during operation of the trailer backup assist system 10, a driver of thevehicle 14 may be limited in the manner in which steering inputs may bemade with the steering wheel 68 of the vehicle 14 due to the powerassist steering system 62 being directly coupled to the steering wheel68. Accordingly, the steering input device 18 of the trailer backupassist system 10 may be used for inputting a desired curvature 26 of thetrailer 12, thereby decoupling such commands from being made at thesteering wheel 68 of the vehicle 14. However, additional embodiments ofthe trailer backup assist system 10 may have the capability toselectively decouple the steering wheel 68 from movement of steerablewheels of the vehicle 14, thereby allowing the steering wheel 68 to beused for commanding changes in the desired curvature 26 of a trailer 12or otherwise selecting a desired backing path during such trailer backupassist.

Referring now to FIG. 7, one embodiment of the steering input device 18is illustrated disposed on a center console 108 of the vehicle 14proximate a shifter 110. In this embodiment, the steering input device18 includes a rotatable knob 30 for providing the controller 28 with thedesired backing path of the trailer 12. More specifically, the angularposition of the rotatable knob 30 may correlate with a desiredcurvature, such that rotation of the knob to a different angularposition provides a different desired curvature with an incrementalchange based on the amount of rotation and, in some embodiments, anormalized rate, as described in greater detail herein.

The rotatable knob 30, as illustrated in FIGS. 7-8, may be biased (e.g.,by a spring return) to a center or at-rest position P(AR) betweenopposing rotational ranges of motion R(R), R(L). In the illustratedembodiment, a first one of the opposing rotational ranges of motion R(R)is substantially equal to a second one of the opposing rotational rangesof motion R(L), R(R). To provide a tactile indication of an amount ofrotation of the rotatable knob 30, a force that biases the knob towardthe at-rest position P(AR) can increase (e.g., non-linearly) as afunction of the amount of rotation of the rotatable knob 30 with respectto the at-rest position P(AR). Additionally, the rotatable knob 30 canbe configured with position indicating detents such that the driver canpositively feel the at-rest position P(AR) and feel the ends of theopposing rotational ranges of motion R(L), R(R) approaching (e.g., softend stops). The rotatable knob 30 may generate a desired curvature valueas function of an amount of rotation of the rotatable knob 30 withrespect to the at-rest position P(AR) and a direction of movement of therotatable knob 30 with respect to the at-rest position P(AR). It is alsocontemplated that the rate of rotation of the rotatable knob 30 may alsobe used to determine the desired curvature output to the controller 28.The at-rest position P(AR) of the knob corresponds to a signalindicating that the vehicle 14 should be steered such that the trailer12 is backed along a substantially straight backing path (zero trailercurvature request from the driver), as defined by the longitudinaldirection 22 of the trailer 12 when the knob was returned to the at-restposition P(AR). A maximum clockwise and anti-clockwise position of theknob (i.e., limits of the opposing rotational ranges of motion R(R),R(L)) may each correspond to a respective signal indicating a tightestradius of curvature (i.e., most acute trajectory or smallest radius ofcurvature) of a path of travel of the trailer 12 that is possiblewithout the corresponding vehicle steering information causing ajackknife condition.

As shown in FIG. 8, a driver can turn the rotatable knob 30 to provide adesired curvature 26 while the driver of the vehicle 14 backs thetrailer 12. In the illustrated embodiment, the rotatable knob 30 rotatesabout a central axis between a center or middle position 114corresponding to a substantially straight backing path 26 of travel, asdefined by the longitudinal direction 22 of the trailer 12, and variousrotated positions 116, 118, 120, 122 on opposing sides of the middleposition 114, commanding a desired curvature 26 corresponding to aradius of the desired backing path of travel for the trailer 12 at thecommanded rotated position. It is contemplated that the rotatable knob30 may be configured in accordance with embodiments of the disclosedsubject matter and omit a means for being biased to an at-rest positionP(AR) between opposing rotational ranges of motion. Lack of such biasingmay allow a current rotational position of the rotatable knob 30 to bemaintained until the rotational control input device is manually movedto a different position. It is also conceivable that the steering inputdevice 18 may include a non-rotational control device that may beconfigured to selectively provide a desired curvature 26 and to overrideor supplement an existing curvature value. Examples of such anon-rotational control input device include, but are not limited to, aplurality of depressible buttons (e.g., curve left, curve right, andtravel straight), a touch screen on which a driver traces or otherwiseinputs a curvature for path of travel commands, a button that istranslatable along an axis for allowing a driver to input backing pathcommands, or a joystick type input and the like.

Referring to FIG. 9, an example of using the steering input device 18for dictating a curvature of a desired backing path of travel (POT) ofthe trailer 12 while backing up the trailer 12 with the vehicle 14 isshown. In preparation of backing the trailer 12, the driver of thevehicle 14 may drive the vehicle 14 forward along a pull-thru path (PTP)to position the vehicle 14 and trailer 12 at a first backup position B1.In the first backup position B1, the vehicle 14 and trailer 12 arelongitudinally aligned with each other such that a longitudinalcenterline axis L1 of the vehicle 14 is aligned with (e.g., parallelwith or coincidental with) a longitudinal centerline axis L2 of thetrailer 12. It is disclosed herein that such alignment of thelongitudinal axis L1, L2 at the onset of an instance of trailer backupfunctionality is not a requirement for operability of a trailer backupassist system 10, but may be done for calibration.

After activating the trailer backup assist system 10 (e.g., before,after, or during the pull-thru sequence), the driver begins to back thetrailer 12 by reversing the vehicle 14 from the first backup position B1. So long as the rotatable knob 30 of the trailer backup steering inputdevice 18 remains in the at-rest position P(AR) and no other steeringinput devices 18 are activated, the trailer backup assist system 10 willsteer the vehicle 14 as necessary for causing the trailer 12 to bebacked along a substantially straight path of travel, as defined by thelongitudinal direction 22 of the trailer 12, specifically the centerlineaxis L2 of the trailer 12, at the time when backing of the trailer 12began. When the trailer 12 reaches the second backup position B2, thedriver rotates the rotatable knob 30 to command the trailer 12 to besteered to the right (i.e., a knob position R(R) clockwise rotation).Accordingly, the trailer backup assist system 10 will steer the vehicle14 for causing the trailer 12 to be steered to the right as a functionof an amount of rotation of the rotatable knob 30 with respect to theat-rest position P(AR), a rate movement of the knob, and/or a directionof movement of the knob with respect to the at-rest position P(AR).Similarly, the trailer 12 can be commanded to steer to the left byrotating the rotatable knob 30 to the left. When the trailer 12 reachesbackup position B3, the driver allows the rotatable knob 30 to return tothe at-rest position P(AR) thereby causing the trailer backup assistsystem 10 to steer the vehicle 14 as necessary for causing the trailer12 to be backed along a substantially straight path of travel as definedby the longitudinal centerline axis L2 of the trailer 12 at the timewhen the rotatable knob 30 was returned to the at-rest position P(AR).Thereafter, the trailer backup assist system 10 steers the vehicle 14 asnecessary for causing the trailer 12 to be backed along thissubstantially straight path to the fourth backup position B4. In thisregard, arcuate portions of a path of travel POT of the trailer 12 aredictated by rotation of the rotatable knob 30 and straight portions ofthe path of travel POT are dictated by an orientation of the centerlinelongitudinal axis L2 of the trailer 12 when the knob is in/returned tothe at-rest position P(AR).

In the embodiment illustrated in FIG. 9, in order to activate thetrailer backup assist system 10, the driver interacts with the trailerbackup assist system 10 and the automatically steers as the driverreverses the vehicle 14. As discussed above, the driver may command thetrailer backing path by using a steering input device 18 and thecontroller 28 may determine the vehicle steering angle to achieve thedesired curvature 26, whereby the driver controls the throttle and brakewhile the trailer backup assist system 10 controls the steering.

With reference to FIG. 10, a method of operating one embodiment of thetrailer backup assist system 10 is illustrated, shown as one embodimentof the operating routine 132 (FIG. 2). At step 134, the method isinitiated by the trailer backup assist system 10 being activated. It iscontemplated that this may be done in a variety of ways, such a making aselection on the display 82 of the vehicle HMI 80. The next step 136,then determines the kinematic relationship between the attached trailer12 and the vehicle 14. To determine the kinematic relationship, variousparameters of the vehicle 14 and the trailer 12 must be sensed, input bythe driver, or otherwise determined for the trailer backup assist system10 to generate steering commands to the power assist steering system 62in accordance with the desired curvature or backing path 26 of thetrailer 12. As disclosed with reference to FIGS. 3-6, the kinematicparameters to define the kinematic relationship include a length of thetrailer 12, a wheel base of the vehicle 14, a distance from a hitchconnection to a rear axle of the vehicle 14, and a hitch angle γ betweenthe vehicle 14 and the trailer 12, among other variables and parametersas previously described. Accordingly, after the kinematic relationshipis determined, the trailer backup assist system 10 may proceed at step160 to determine the current hitch angle by processing the hitch angleestimation routine 130.

As shown in FIG. 11, one embodiment of a kinematic relationship betweenthe trailer 12 an the vehicle 14 is developed with the illustratedschematic diagram that shows the geometry of a vehicle and a traileroverlaid with a two-dimensional x-y coordinate system, identifyingvariables, such as the trailer yaw rate ω₂ and the vehicle yaw rate ω₁,which are used to determine the corresponding hitch angle γ. As such,hitch angle estimation may be determined using trailer yaw rate signalω₂, vehicle speed signal v₁ and vehicle yaw rate signal ω₁. Morespecifically, the yaw rate of the trailer is given by the followingkinematic equation:

$\omega_{2} = {{\frac{v_{1}}{D}\sin \; \gamma} - {\frac{L}{D}\cos \; {\gamma\omega}_{1}}}$

This kinematic equation can be rearranged to estimate trailer hitchangle γ, as follows:

$\gamma = {\sin^{- 1}\frac{{v_{1}\omega_{2}D} + {\omega_{1}L\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}} - {\omega_{2}^{2}D^{2}}}}}{v_{1}^{2} + {\omega_{1}^{2}L^{2}}}\mspace{14mu} {or}}$$\gamma = {{\sin^{- 1}\frac{\omega_{2}D}{\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}}}}} + {\tan^{- 1}\frac{\omega_{1}L}{v_{1}}}}$

Referring to FIG. 12, one embodiment of the hitch angle estimationroutine 130 is illustrated, whereby the above-noted kinematicrelationship is utilized to instantaneously estimate the hitch angle γ.At step 138, the sensor signals are received for executing the steps todetermine the hitch angle γ. The sensor signals may include the traileryaw rate signal ω₂, the vehicle speed signal v₁, and the vehicle yawrate signal ω₁, along with other sensor signals that may be used in someembodiments, such as the steering angle δ signal, trailer lateralacceleration a_(y2), the measure hitch angle from the hitch angle sensor44 among other potential sensor signals. At step 140, these signals maybe filtered and any potential offsets may be compensated beforeproceeding to further process the sensor signals.

Still referring to FIG. 12, in one embodiment, the vehicle speed v₁ maybe received from the speed sensor 58 on the vehicle 14 and not requireany further processing or derivation to proceed with calculating theinstantaneous hitch angle γ. However, at step 142, in some embodiments,the vehicle speed v₁ may be derived from wheel speed sensors on thevehicle 14, the positioning device 56, or other conceivable means todetermine the vehicle speed v₁. Also, according to one embodiment, thevehicle yaw rate ω₁ may be received directly from the yaw rate sensor 60on the vehicle 14 and not necessitate any further derivation. However,it is also contemplated that at step 142, the vehicle yaw rate ω₁ mayadditionally or alternatively be derived from left and right wheel speedsensors on the vehicle 14. Further, according to an additionalembodiment, the vehicle yaw rate ω₁ may be derived from the steeringangle δ of the vehicle 14 and the vehicle speed v₁, along with thevehicle wheelbase W, which is known or otherwise stored in the memory 86of the controller 28. One embodiment of an equation to determine thevehicle yaw rate ω₁ based on the steering angle δ and the vehicle speedv₁ is as follows:

$\omega_{1} = {{- \frac{v_{1}}{W}}\tan \; {\delta.}}$

As shown in FIG. 12, the trailer yaw rate ω₂ may also be provideddirectly by the sensor system 16 at step 138 or determined fromprocessing the sensor signals at step 142. For instance, the trailer yawrate ω₂ may be received directly from the yaw rate sensor 25 mounted onthe trailer 12. Additionally or alternatively, the trailer yaw rate ω₂may be derived from the left and right wheel speed sensors 23 on thetrailer 12. Also, in addition or in the alternative, the trailer yawrate ω₂ may be calculated using the trailer speed v₂ and the lateralacceleration a_(y2) of the trailer, as sensed by the accelerometer 27 ofthe trailer sensor module 20, in one embodiment. One embodiment of suchan equation to determine the trailer yaw rate ω₂ is as follows, wherelateral acceleration a_(y2) of the trailer may be derived from theaccelerometer 27 and trailer speed v₂ may be derived from the wheelspeed sensor 23:

$\omega_{2} = {\frac{a_{y\; 2}}{v_{2}}.}$

When wheel speed sensors 23 are not available or otherwise included onthe trailer sensor module 20 or the sensor system 16, theabove-referenced kinematic equation may then be reordered to solve forthe trailer speed v₂, as follows:

v ₁ ²+ω₁ ² L ² −D ²ω₂ ²=(v ₁ cos γ+L sin γω₁)² =v ₂ ² , v ₂=√{squareroot over (v ₁ ²+ω₁ ² L ² −D ²ω₂ ²)}.

As such, the accuracy of the trailer speed v₂ and the resultantcalculated hitch angle γ will rely more heavily on the accuracy of theother sensors utilized to determine the vehicle speed v₁, vehicle yawrate and the trailer yaw rate ω₂, as previously mentioned, along withthe accuracy of the vehicle and trailer dimensions L and D.

As illustrated in FIG. 12, when the sensor signals have been receivedand the necessary parameters received or otherwise determined, at step144, the controller 28 processes the following equation, based on thekinematic relationship of the trailer 12 and the vehicle 14, to solvefor the instantaneous hitch angle γ.

$\gamma = {\sin^{- 1}\left( \frac{{v_{1}\omega_{2}D} + {\omega_{1}L\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}} - {\omega_{2}^{2}D^{2}}}}}{v_{1}^{2} + {\omega_{1}^{2}L^{2}}} \right)}$

Further, should the sensor system 16 be unequipped to provide thecontroller 28 with the trailer yaw rate ω₂, in another embodiment, atstep 144, the instantaneous hitch angle γ may still be determined, asfollows:

$\gamma = {\sin^{- 1}\frac{{v_{2}\omega_{1}L} \pm {v_{1}\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}} - v_{2}^{2}}}}{v_{1}^{2} + {\omega_{1}^{2}L^{2}}}\mspace{14mu} {or}}$$\gamma = {{\sin^{- 1}\frac{v_{2}}{\sqrt{v_{1}^{2} + {\omega_{1}^{2}L^{2}}}}} - {\tan^{- 1}{\frac{v_{1}}{\omega_{1}L}.}}}$

In this equation, the hitch angle γ is determined based on the vehiclespeed v₁, trailer speed v₂, and vehicle yaw rate ω₁, whereby suchparameters are relied upon more heavily for accuracy. The above equationsolving for the hitch angle γ is based on a kinematic relationship forthe trailer speed v₂, which does not incorporate the trailer yaw rateω₂, as follows:

v ₂ =v ₁ cos γ+L sin γω₁.

With this identified relationship, it is conceivable that if the hitchangle is known by another means, such the hitch angle sensor 44, thetrailer speed v₂ may also be solved for with the above equation.

Also, trailer speed v₂ may be determined with the following equation,based on the trail yaw rate ω₂ and the lateral acceleration a_(y2) ofthe trailer, such as from the trailer yaw rate sensor 25 and theaccelerometer 27, respectively.

$v_{2} = \frac{a_{y\; 2}}{\omega_{2}}$

Accordingly, when the trailer speed v₂ is sensed or otherwise determinedfrom other variables, such as the trail yaw rate ω₂ and the lateralacceleration a_(y2) of the trailer, then the hitch angle γ calculationmay incorporate this parameter, as follows:

$\gamma = {\sin^{- 1}{\frac{{v_{1}\omega_{2}D} + {v_{2}\omega_{1}L}}{v_{1}^{2} + {\omega_{1}^{2}L^{2}}}.}}$

Referring again to FIG. 12, at step 146 the presently estimated hitchangle γ may be filtered to provide a more accurate estimate. Morespecifically, the hitch angle γ estimated with the hitch angleestimation routine 130 may be less accurate at low vehicle speed v₁ whenthe denominator of the above-noted equations approaches zero. In oneembodiment, the hitch angle γ may be filtered by using the trailer yawrate ω₂ and the vehicle yaw rate ω₁. For instance, the estimated hitchangle γ could be filtered with a discrete-time Kalman filter, wherebythe filtered hitch angle estimate is obtained from the followingequation:

{circumflex over (γ)}_(k-1)={circumflex over(γ)}_(k)+(ω_(2,k)−ω_(1,k))·T _(s) +K _(k)·(γ_(k)−{circumflex over(γ)}_(k)).

In this embodiment, T_(s) is the sampling time, k is an integerrepresenting the k^(th) sampling instance, K_(k) is the Kalman gain, andγ_(k) is the calculated hitch angle from the above-noted equations.

However, when the vehicle 14 is stopped, the filtered estimate is“frozen” at the previously known good value, i.e.:

{circumflex over (γ)}_(k-1)={circumflex over (γ)}_(k).

This is the filter to determine when the vehicle 14 is stopped ortraveling at low speeds, as provided at step 148, which precedes step144. If the vehicle 14 is not determined to be stopped or traveling slowat step 148, the hitch angle γ is estimated and filtered at steps 144and 146, as described above. When the result of an accurate hitch angleγ from the above-noted kinematic equations is temporarily not availableor inaccurate (e.g., at low speed), the filtered estimate is obtainedfrom the following equation:

{circumflex over (γ)}_(k-1)={circumflex over(γ)}_(k)+(ω_(2,k)−ω_(1,k))·T _(s).

In an additional or alternative embodiment, the hitch angle γ may befiltered by using the vehicle yaw rate ω₁ and vehicle speed v₁. Forinstance, this may be desired if the trailer yaw rate ω₂ is noisy,whereby the filtering described above and shown in FIG. 12 may notgenerate desired results. In this case, the since the diagramillustrated in FIG. 11 is nonlinear, a nonlinear extension of the Kalmanfilter, which is often referred to as extended Kalman filter by thoseskilled in the art, may be applied. To do so, when the results aregenerally available and accurate for the hitch angle γ determined atstep 144, such as when the vehicle 14 is moving a sufficient speed, thefilter hitch angle may be estimated from the following equation:

${\hat{\gamma}}_{k + 1} = {{\hat{\gamma}}_{k} + {\left( {{\frac{v_{1,k}}{D}\sin \; {\hat{\gamma}}_{k}} - {\frac{\omega_{1,k} \cdot L}{D}\cos \; {\hat{\gamma}}_{k}} - \omega_{1,k}} \right) \cdot T_{s}} + {K_{k} \cdot \left( {\gamma_{k} - {\hat{\gamma}}_{k}} \right)}}$

Accordingly, when the results are temporarily not available orinaccurate for the hitch angle γ determined at step 144, such as at lowspeeds, the filtered hitch angle estimate may is obtained from thefollowing equation:

${\hat{\gamma}}_{k + 1} = {{\hat{\gamma}}_{k} + {\left( {{\frac{v_{1,k}}{D}\sin \; {\hat{\gamma}}_{k}} - {\frac{\omega_{1,k} \cdot L}{D}\cos \; {\hat{\gamma}}_{k}} - \omega_{1,k}} \right) \cdot T_{s}}}$

There are many alternative ways to express the Kalman gain, and one ofthe formulations is given as follows:

${A_{k} = {{\left( {{\frac{v_{1,k}}{D}\cos \; {\hat{\gamma}}_{k}} + {\frac{\omega_{1,k} \cdot L}{D}\sin \; {\hat{\gamma}}_{k}}} \right) \cdot T_{s}} + 1}},{K_{k} = {P_{k}\left( {P_{k} + R} \right)}^{- 1}},{P_{k + 1} = {{{A_{k}\left( {1 - K_{k}} \right)}P_{k}A_{k}^{T}} + Q}},$

where A_(k) is the derivative matrix, Q is the process noise covariance,R is the measurement noise covariance, and P_(k) is the estimation errorcovariance.

As shown in FIG. 12, upon estimating and filtering the hitch angle γ, atstep 152 the trailer length D and vehicle wheelbase W can be estimatedor refined to improve the accuracy of later calculations. As such,trailer length D may be estimated based on the trailer speed v₂, thevehicle speed v₁, the vehicle yaw rate ω₁, and the trailer yaw rate ω₂,as determined from the previous steps of the hitch angle estimationroutine 130. For instance, if the drawbar length L between hitch pointand rear axle of the vehicle 14 is measured or otherwise known, thetrailer length D can be calculated as follows:

$D = {\sqrt{\frac{v_{1}^{2} + {\omega_{1}^{2}L^{2}} - v_{2}^{2}}{\omega_{2}^{2}}}.}$

Similarly, if the trailer length D is measured or otherwise known, thedrawbar length L between hitch point and rear axle of the vehicle 14 maybe estimated based on the trailer speed v₂, the vehicle speed v₁, thevehicle yaw rate ω₁, and the trailer yaw rate ω₂, as determined from theprevious steps of the hitch angle estimation routine 130. As such, thedrawbar length L can be calculated as follows:

$L = {\sqrt{\frac{v_{2}^{2} + {\omega_{2}^{2}D^{2}} - v_{1}^{2}}{\omega_{1}^{2}}}.}$

As also shown in FIG. 12, at step 154 the hitch angle estimation routine130 may proceed to estimate or refine the trailer turning radius r₂ andthe curvature κ₂ of the trailer trajectory for improving the accuracy oflater calculations. This may be done using the following equations:

${r_{2} = \frac{v_{2}}{\omega_{2}}},{and}$$\kappa_{2} = {\frac{\omega_{2}}{v_{2}}.}$

Referring again to FIG. 10, at step 160 the hitch angle γ is determinedbetween the vehicle 14 and the trailer 12, although this may be donecontinuously during operation of the trailer backup assist system 10. Itis contemplated that in additional embodiments of the trailer backupassist system 10 that the steps of determining the kinematicrelationship and sensing the hitch angle γ may occur before the trailerbackup assist system 10 is activated or at any other time beforesteering commands are generated. Accordingly, at step 162, the positionand rate of changes is received from the steering input device 18, suchas the angular position and rate of rotation of the rotatable knob 30,for determining the desired curvature 26. At step 164, steering commandsmay be generate based on the desired curvature, correlating with theposition and rate of change of the steering input device 18. Thesteering commands and actuation commands generated may be generated inconjunction with processing of the curvature routine 98, as previousdiscussed. At step 166, the steering commands and actuation commandshave been executed to guide the trailer 12 on the desired curvatureprovided by the steering input device 18.

In parallel with performing the operations for receiving the trailerbackup assist requests, determining the desired curvature 26 of thetrailer 12, and generating the vehicle steering commands, the trailerbackup assist system 10 may perform an operation for monitoring if anunacceptable trailer backup condition exists. Examples of suchmonitoring include, but are not limited to assessing a hitch angle γ todetermine if a hitch angle γ threshold is exceeded, assessing a backupspeed to determine if a backup speed threshold is exceeded, assessingvehicle steering angle to determine if a vehicle steering anglethreshold is exceeded, assessing other operating parameters (e.g.,vehicle longitudinal acceleration, throttle pedal demand rate and hitchangle rate) for determining if a respective threshold value is exceeded,and the like. Backup speed can be determined from the wheel speedinformation obtained from one or more speed sensors 58 of the vehicle14. If it is determined that an unacceptable trailer backup conditionexists, an operation may be performed for causing the current path oftravel of the trailer 12 to be inhibited (e.g., stopping motion of thevehicle 14), followed by the operation being performed for ending thecurrent trailer backup assist instance. It is disclosed herein thatprior to and/or in conjunction with causing the current trailer path tobe inhibited, one or more actions (e.g., operations) can be implementedfor providing the driver with feedback (e.g., a warning) that such anunacceptable hitch angle condition is impending or approaching. In oneexample, if such feedback results in the unacceptable hitch anglecondition being remedied prior to achieving a critical condition, themethod can continue with providing trailer backup assist functionalityin accordance with operations. Otherwise, the method can proceed tooperation for ending the current trailer backup assist instance. Inconjunction with performing the operation for ending the current trailerbackup assist instance, an operation can be performed for controllingmovement of the vehicle 14 to correct or limit a jackknife condition(e.g., steering the vehicle 14, decelerating the vehicle 14, limitingmagnitude and/or rate of driver requested trailer curvature input,limiting magnitude and/or rate of the steering command, and/or the liketo preclude the hitch angle from being exceeded).

With the sensor system 16 and/or controller 28 providing the trailer yawrate ω₂, this parameter may additionally or alternatively be utilized toimprove the electronic stability control provided with the power assiststeering system 62 when the vehicle 14 is towing a trailer. Someelectronic stability control systems use a so called bicycle model(without trailer) to obtain a reference vehicle yaw rate commanded bythe driver. However, when the vehicle is towing a trailer, the towingvehicle may exhibit more oversteer or more understeer tendencies duringa turn, compared to the same vehicle without a trailer attached. Thusthe electronic stability control performance may degrade, and/orunintended activations may occur, when the vehicle is towing a trailer.

By using the sensed or otherwise determined trailer yaw rate signal ω₂,together with other electronic stability control signals, the additionaloversteer or understeer tendencies of the vehicle (compared to when nottowing a trailer) can be identified. Accordingly, the existingelectronic stability control system can be sensitized or desensitized(e.g., by modifying the control thresholds for the brake and enginecontrollers). The brake and engine control actions can also be increasedor reduced by changing the controller gains. Therefore, an additionalcontroller which uses trailer yaw rate signal ω₂ (or the differencebetween trailer and vehicle yaw rate, i.e., ω₂−ω₁) and its derivativemay be integrated with the existing electronic stability control system.Such a controller is beneficial for improving the overallvehicle-trailer combination stability

In addition, it is contemplated that using the trailer yaw rate signalω₂ and trailer lateral acceleration signal a_(y2), together with otherstandard electronic stability control signals, may further identifyadditional oversteer or understeer tendencies of the vehicle. It is alsoconceivable that a controller that uses the trailer hitch angle γ as afeedback signal may be integrated with the existing electronic stabilitycontrol system for improving the overall vehicle-trailer combinationstability.

As previously mentioned, the hitch angle γ determined by the hitch angleestimation routine 130 may also be used to identify and stabilize aswaying trailer. More specifically, the vehicle-trailer combinationbecomes less damped when its speed is increased. With any driver inputsor external disturbances, the trailer may start to oscillate and theoscillation may sustain for a long time. If the speed is above certain“critical speed”, the system may become unstable, causing theoscillation amplitude to grow larger and eventually cause vehicleinstability and/or a jackknife condition. A controller which usestrailer yaw rate signal ω₂ (or the difference between trailer andvehicle yaw rate, i.e., ω₂−ω₁) and its derivative can be designed toactively control the vehicle/trailer to damping out the oscillation. Inaddition, the trailer yaw rate ω₂ and the trailer lateral accelerationa_(y2), together with other standard electronic stability controlsignals, may be used to stabilize a swaying trailer. Since both traileryaw rate signal ω₂ and trailer lateral acceleration signal a_(y2)directly provide information about the trailer motion, they can be usedto quickly identify whether the trailer is swaying.

As discussed above, the hitch (trailer) angle γ can be estimatedutilizing yaw rate measurements. However, if the vehicle 14 and trailer12 are stationary, the yaw rate will be zero, and the trailer backupassist system 10 cannot therefore estimate a hitch angle γ utilizing yawrate measurements when the vehicle 14 and trailer 12 are stationary. Thecontroller 28 of trailer backup assist system 10 may be configured tocontinuously calculate and update the estimated hitch angle duringoperation utilizing measured yaw rate data. If the vehicle 14 andtrailer 12 stop, the trailer hitch angle γ estimated prior to stoppingthe vehicle can be stored and reused when the vehicle 14 and trailer 12begin moving. With reference to FIG. 13, the hitch angle γ can be storedin non-volatile memory if the authentication device 202 changes from aON state to an OFF state (i.e. a KEY OFF or power off event occurs), andthe hitch angle γ can be retrieved at the next KEY ON or power on event(i.e. authentication device 202 changes from an OFF state to an ONstate).

Also, the trailer length D and the drawbar length L can be calculated(estimated) utilizing sensor data (e.g. yaw rate data) obtained whilethe vehicle 14 and trailer 12 are moving as discussed above inconnection with FIG. 12. Trailer data (e.g. trailer length D, drawbarlength L, etc.) can also be stored in non-volatile memory at the timethe vehicle is turned off as indicated by a KEY OFF event. It will beunderstood that measured trailer data (e.g. trailer length D and drawbarlength L) that has been input by a user rather than estimated by system10 may also be stored when vehicle 14 is turned off, and retrieved whenvehicle 14 is turned on.

Referring again to FIG. 13, a system and method 200 for enhanced yawrate trailer angle detection initialization 200 involves determining ifa vehicle is turned on at step 206. Step 206 may include determining ifthe vehicle ignition is ON based on a signal from the authenticationdevice 202. If the vehicle was turned OFF at step 232 (i.e. a KEY OFF(power off) event occurred), step 206 may include determining if theauthentication device 202 has changed from an OFF state to an ON state,thereby defining a KEY ON (power on) event. If the vehicle has not beenturned ON at step 206, no action is taken. However, if the vehicle hasbeen turned on, trailer data is retrieved from non-volatile memory asshown at step 208. The retrieved trailer data may comprise uniquetrailer identification information, vehicle position data, trailer angleγ, trailer length L, hitch location, trailer mileage, and aTrailerConnected Flag as shown at step 234 that had previously beenstored as shown at step 234.

It will be understood that the power turned off (step 234) and on (step206) may comprise only power off/on to system 10, or power off/on maycomprise the main power to vehicle 14 being off/on. Typically, power tosystem 10 is tied directly to main vehicle electrical power such thatelectrical power is supplied to system 10 when vehicle main power is on,and power is not supplied to system 10 when the vehicle main electricalpower is off. However, power could also be supplied to system 10independently of main vehicle electrical power being on or off.

At steps 210 and 212, the controller 28 determines if trailer 12 isconnected to vehicle 14. As discussed above, this may be accomplishedutilizing trailer present sensor 204 (FIG. 2) and/or signals from one ormore of sensors 23, 25, and 27 of trailer sensor module 20. If a trailerconnection is not detected at step 212, a TrailerConnected Flag is setto FALSE as shown at step 236 and no additional action is taken by thesystem 10. However, if a trailer connection is detected at step 212, theTrailerConnected Flag is set to TRUE at step 214.

After the TrailerConnected Flag is set to TRU at step 214, thecontroller 28 of trailer backup assist system 10 compares currenttrailer identification information to trailer identification informationthat was previously stored at step 234 when the vehicle was turned off(i.e. a KEY OFF event). The trailer identification information maycomprise serial numbers that are unique to one or more of the sensors23, 25, and 27 of trailer sensor module 20. Alternatively, the traileridentification information may comprise other unique identificationinformation (e.g. a bar code on target 52) that can be utilized by thecontroller 28 of trailer backup assist system 10 to determine if thetrailer 12 that is presently connected to vehicle 14 is identical to thetrailer 12 that was present at the time the vehicle was turned off (KEYOFF) at step 232.

If the identification information info is not equal to memory at step216, trailer setup 238 is initiated. Trailer setup 238 may comprise aprocess including providing a signal to an operator utilizing screen 82indicating that trailer 12 must be connected, and that trailer lengthand other data must be entered or that the vehicle must be driveninitially to provide the trailer backup assist system 10 with data thatcan be utilized to learn (estimate) the trailer length and otherparameters.

If the trailer identification information is equal to the stored traileridentification information at step 216, the controller 28 of trailerbackup assist system 10 then determines the current (present) vehicleposition at step 218. The vehicle position 218 may be determinedutilizing a GPS system on vehicle 14. At step 220, The current vehicleposition is compared to a prior vehicle position that was stored at step234 when the vehicle 14 was previously turned off at step 232. At step220, if the current vehicle position is substantially equal to thestored vehicle position, the trailer hitch angle is initialized as shownat step 222. However, if the controller 28 of system 10 determines atstep 220 that the vehicle 14 has moved since the last KEY OFF, trailersetup 238 is initialized. In this way, the controller 28 “assumes” thatthe trailer angle previously stored at step 238 is no longer accurate ifthe vehicle has moved as determined at step 220.

If the vehicle 14 has not moved, and if the hitch angle is initializedas shown at step 222, the controller 28 retrieves the trailer data asshown at step 224. The trailer data retrieved at step 224 may correspondto the data stored at step 234, and may include the trailer angle,trailer length, hitch location, and any other data that may be requiredby trailer backup assist system 10 to begin trailer backup operations.It will be understood that step 224 would not necessarily requireretrieving trailer data from non-volatile memory if the trailer data haspreviously been retrieved. For example, the trailer data may beretrieved prior to step 224, and step 224 may involve an “authorization”to utilize the previously retrieved data during trailer backupoperations.

After the trailer data is retrieved at step 224, or after the trailersetup 238 is completed, the trailer backup assist system 10 is activatedas shown at step 226. As shown at step 228, if the vehicle 14 is parked,the trailer backup assist system 10 then determines if the trailer isdisconnected at step 230. The trailer disconnection of step 230 may besubstantially the inverse of the trailer connection determination ofstep 212, and it may involve determining if sensor 208 has indicatedthat a trailer 12 is connected. Step 230 may also include determining ifcontroller 28 has established an electrical connection with trailersensor module 20. If the trailer 12 is disconnected at step 230, theprocess returns back to step 226. If the trailer is not disconnected atstep 230, the process continues to step 232. At step 232, the systemdetermines if the vehicle 14 is turned off. This may involve determiningif authentication device 202 is in an OFF state, or if authenticationdevice 202 has changed from an ON state to an OFF state to define a KEYOFF (power off) event. If the vehicle 14 is not parked at step 228, thetrailer backup assist system 10 operates to control/assist trailerbackup as described in more detail above in connection with FIGS. 1-12.

If the vehicle has been turned off at step 232, the process thencontinues to step 234. At step 234, trailer data, vehicle position,trailer angle γ, trailer length L, hitch location, trailer mileage, andthe TrailerConnected Flag are stored in non-volatile memory. It will beunderstood that not all of the trailer data shown at step 234 in FIG. 13would necessarily have to be stored in every case. Alternatively, otherdata such as a trailer image pattern generated by camera 46 could alsobe stored.

The system and process 200 shown in FIG. 13 solves problems associatedwith turning a vehicle on and off, disconnecting a trailer, etc. byenabling the trailer backup assist system 10 to determine if a specifictrailer has remained connected to vehicle 14 during a period of time inwhich the vehicle was turned off. The process shown in FIG. 13 solvesthe problem by storing trailer identification information along withtrailer connection state, vehicle position (optional), trailer/hitchangle γ, trailer length L, hitch position (drawbar length L), andtrailer image pattern (optional if the vehicle is equipped) when thevehicle is parked and turned off, and comparing these data at KEY ON(power on) to determine if the same trailer 12 is still connected at thesame trailer angle γ. In turn, the trailer parameters and trailer angleγ may be available to the trailer backup assist system 10 without theneed for trailer setup (step 238) or calibration driving.

As discussed above, a trailer connection (step 212) may be detected whenan electrical connection is active between vehicle 14 and trailer 12. Asalso discussed above, the trailer backup assist system may be configuredto retrieve trailer identification information from the last key cycle(i.e. data stored at step 234 when the vehicle is turned off at step238). Retrieving the trailer identification information may beaccomplished by reading a serial number from one or more of the sensors23, 25, and 27 of trailer sensor module 20 or a unique serial number orother identification data associated with the trailer 12 itself. If thetrailer identification information substantially matches the valuestored at step 234 by trailer backup assist system 10, the system 10retrieves the vehicle position as discussed above in connection withstep 218. If the trailer 12 has remained connected since the last keycycle and/or the vehicle position has not changed since the last keycycle, the trailer angle γ is also assumed to be unchanged as discussedabove in connection with steps 220 and 222 of FIG. 13. In turn, trailerangle detection is initialized at step 226 utilizing thepreviously-stored trailer hitch angle.

With reference to FIG. 14, an angle measuring device includes an arrowmember 240 that may be attached to trailer 12 (or vehicle 14) and anarcuate member 242 that may be attached to vehicle 14 (or trailer 12) topermit a user to visually determine a trailer angle that can be input atstep 238 (FIG. 13). Trailer 12 pivots about vertical axis 42 relative tovehicle 14, thereby causing pointed end 248 of arrow member 240 to pointat indicia 244 of arcuate member 242. Indicia 244 may comprise angles“10°,” “−10°,” etc. to thereby permit a user to readily determine(measure) an initial trailer angle that can be input prior to use ofsystem 10 if the vehicle has moved (step 220) such that a stored trailerangle (step 234) cannot be retrieved at steps 222 and 224. Arrow member240 and arcuate member 242 may be made from sheets of polymer or othersuitable material, and may be attached to trailer 12 and vehicle 14utilizing adhesive, mechanical fasteners, or other suitable connectors.

It will be understood by one having ordinary skill in the art thatconstruction of the described invention and other components is notlimited to any specific material. Other exemplary embodiments of theinvention disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein.

For purposes of this disclosure, the term “coupled” (in all of itsforms, couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature or may be removableor releasable in nature unless otherwise stated.

It is also important to note that the construction and arrangement ofthe elements of the invention as shown in the exemplary embodiments isillustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multiple partsor elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures and/or members or connector or otherelements of the system may be varied, the nature or number of adjustmentpositions provided between the elements may be varied. It should benoted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present invention. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present invention, and further it is to beunderstood that such concepts are intended to be covered by thefollowing claims unless these claims by their language expressly stateotherwise.

What is claimed is:
 1. A vehicle including a trailer backup assist system, the vehicle comprising: an authentication device that permits vehicle operation if the authentication device is actuated to an ON state from an OFF state; a sensor that is configured to provide a signal indicating whether or not a trailer is attached to the vehicle; a controller configured to: store trailer data, a vehicle position and hitch angle if the authentication device changes from an ON state to an OFF state to define a power off event; determine if the authentication device has changed from an OFF state to an ON state to define a power on event; determine if a trailer is connected to the vehicle if a power on event occurs; determine if a present position of the vehicle has changed since a power off event; determine if a present position of the vehicle has not changed, retrieve at least one of trailer data and hitch angle for use in the trailer backup assist system; determine if a present position of the vehicle has not changed since a power off event, to provide an indication to a user that trailer data needs to be supplied to the trailer backup assist system.
 2. The vehicle of claim 1, wherein: the controller is configured to retrieve the trailer data only if a trailer is attached to the vehicle.
 3. The vehicle of claim 1, wherein: the trailer data comprises a trailer dimension.
 4. The vehicle of claim 1, wherein: the controller is configured to store unique trailer identification information prior to a power off event and to retrieve stored unique trailer identification information after a power on event to thereby determine if a trailer detected after a power on event is a different trailer than a trailer connected prior to a power off event.
 5. The vehicle of claim 4, wherein: the unique trailer identification information comprises a unique code.
 6. The vehicle of claim 5, wherein: the unique code comprises a serial number of a sensor mounted to the trailer.
 7. The vehicle of claim 1, wherein: the controller is configured to determine a calculated hitch angle utilizing data from a yaw rate sensor that senses a yaw rate of a trailer relative to the vehicle; and the controller is configured to store the calculated hitch angle prior to a power off event.
 8. The vehicle of claim 7, wherein: the yaw rate sensor comprises a camera.
 9. The vehicle of claim 7, wherein: the yaw rate sensor comprises a piezoelectric device.
 10. The vehicle of claim 1, wherein: the trailer backup assist system is configured to calculate a hitch angle utilizing data from a yaw rate sensor.
 11. The vehicle of claim 10, wherein: the trailer backup assist system is configured to continuously update a stored hitch angle unless the vehicle has stopped moving or if the vehicle power is turned off.
 12. A vehicle, comprising: a trailer backup assist system having a controller configured to: estimate a hitch angle using yaw rate data; store information including a trailer dimension, vehicle position, trailer connected flag, and hitch angle in non-volatile memory, and retrieve the information when the vehicle is turned on; compare the retrieved information to corresponding current information and utilize the retrieved information for trailer backup assist control if the vehicle has not moved.
 13. The vehicle of claim 12, wherein: the controller only utilizes the retrieved information if the retrieved trailer connected flag and a current trailer connected flag are both true.
 14. The vehicle of claim 13, wherein: the controller is configured to receive unique trailer identification information from a trailer and store the unique trailer identification information in non-volatile memory.
 15. The vehicle of claim 14, wherein: the controller is configured to: retrieve unique trailer identification information from non-volatile memory after the vehicle is turned on and compare the retrieved unique trailer identification information to current unique trailer identification information received from a trailer; utilize the retrieved trailer dimension for trailer backup assist control only if the retrieved unique trailer identification information is substantially identical to the current unique trailer identification information.
 16. The vehicle of claim 15, wherein: the unique trailer identification information comprises at least one of a serial number of a sensor and image data for a trailer.
 17. The vehicle of claim 12, wherein: the controller is configured to generate a signal prompting a user to provide trailer data if the vehicle has moved and including: a mechanical trailer angle measuring device having first and second members that provides a visual indication of a trailer angle.
 18. The vehicle of claim 12, wherein: the controller is configured to receive steering request data from a rotatable knob mounted in an interior of the vehicle as a control input during backup operations with a trailer attached to the vehicle.
 19. The vehicle of claim 12, wherein: the controller is configured to generate a signal prompting a user to perform a calibration maneuver if the vehicle has moved.
 20. The vehicle of claim 12, wherein: the controller is configured to generate a signal prompting a user to provide trailer angle if the vehicle has moved. 